Apparatus for holding electrically non-conductive material and improving electron beam cutting thereof



Dec. 17, 1968 P. CANNON ETAL 3,417,222

APPARATUS FOR HOLDING ELECTRICALLY NON-CONDUCTIVE MATERIAL AND IMPROVINGELECTRON BEAM CUTTING THEREOF Filed March 1, 1965 VA C UUM PUMP/N G-SYSTEM [nvent'or-s:

eter Cannon, Will/am R.Grdms, William L. Mowr-ey,

he/r Attorney.

United States Patent 3,417,222 APPARATUS FOR HOLDING ELECTRICALLYNON-CONDUCTIVE MATERIAL AND IMPROV- ING ELECTRON BEAM CUTTING THEREOFPeter Cannon, Alplaus, William R. Grams, Ballston Spa, and William L.Mowrey, Scotia, N.Y., assignors to General Electric Company, acorporation of New York Filed Mar. 1, 1965, Ser. No. 436,009 5 Claims.(Cl. 219121) ABSTRACT OF THE DISCLOSURE An apparatus is described forcontrolled cutting or drilling of a hard non-conducting material suchas, for example, diamond by the use of a high energy beam of electronsfocused in a vacuum work chamber. The workpiece is supported andenclosed by an adjustable vise member made of a metal having a high rateof thermal and electrical conductivity. The wise includes a cavitywithin a base portion thereof which serves as an effectiveelectron-trapping cage. A very small expansion nozzle is mounted in thework chamber for accurately impinging flow of an appropriate gas uponthe focal point of the electron beam upon the workpiece.

This invention relates to improvements in apparatus for and a method ofcutting and drilling hard materials by electron beam techniques, andmore specifically to the cutting of diamond crystals at greatlyincreased rates employing apparatus of simplified construction.

Various methods have been devised for machining diamonds, i.e. cleaving,bruting, sawing and scaife grinding as well as electron beam cutting. Itis well known that much time and patience are required for diamondshaping by the earlier well-known processes and it is also known thatthe complicated and expensive apparatus proposed to date for theelectron beam cutting of diamonds have prevented the latter method fromacquiring commercial acceptance.

It is therefore a primary object of this invention to provide simplifiedapparatus for cutting a hard crystal under the combined effects ofelectron beam impact and gas impingement whereby wide variations in gasmaterials and concentration, beam current and potential are readilyavailable for cutting various very hard materials with maximumeffectiveness.

It is another object of this invention to provide an apparatus for andmethod of cutting a diamond crystal enabling the use of greatlysimplified and less expensive equipment and yet at commerciallyattractive cutting rates.

It is another object of this invention to provide a novel vise forholding a nonconducting crystal for the cutting thereof by the use of anelectron beam.

The aforementioned and other objects are provided in the practice ofthis invention by using an apparatus comprising in combination anelectron emitter, electron optics and control means for focusing astream of electrons from said emitter, a working chamber within whichthe stream of electrons from the electron emitter is focused on theworkpiece, a single vacuum pumping system, a very small expansion nozzlehaving a large length/ area ratio mounted in said chamber for accuratelyimpinging a flow of an appropriate gas upon the point of focus on saidworkpiece and a vise construction having particular thermal andelectrical properties for holding the workpiece during the cuttingoperation.

The practice of this invention is particularly well illustrated by theemployment thereof to cut diamond material either as single crystal oras polycrystalline masses.

3,417,222 Patented Dec. 17, 1968 In the case of diamond-cutting thepreferred gas for impingement is oxygen although carbon dioxide willalso readily oxidize diamond at higher temperatures. In those instancesin which it is proposed to cut other very hard materials by this methodit may easily be determined whether some particular gas will beeffective for accelerating the cutting action either as a decompositioncatalyst or simply to accelerate gasification of the material in thecutting region. If no such advantageous action is afforded by any knowngas such a jet of gas will at least serve to blow away the debrisengendered by the electron beam during cutting.

The exact nature of this invention as well as other objects andadvantages thereof will be readily apparent from consideration of thefollowing specification relating to the annexed drawing in which:

FIG. 1 is a vertical cross section of one form of the electron beamgenerating device that may be used in the practice of this inventiontogether with the gas lance and vise combined therewith in accordancewith this invention; and

FIG. 2 is an isometric view of a preferred embodiment of a viseconstructed in accordance with this invention showing in greater detailthe simultaneous superimposition of the very fine stream of gas upon theimpact area of the electron beam on the workpiece.

Electrons to eifect the cutting action in the practice of this inventionmay be provided by an electron beam welder, such as a Hamilton-Zeisselectron beam welder No. ESl002A as manufactured by Hamilton-Electrona,Inc. Such an electron beam welding apparatus 10 is representedschematically in FIG. 1 and is ordinarily used commercially to jointogether materials such as refractory metals, ceramics, dissimilarmetals, steels, aluminum, etc. utilizing a high energy density focusedbeam of electrons.

In essence, the electron gun 11 consists of a cathode, heated tungstenfilament 12, an electrostatic beam collimating electrode or grid 13 andapertured anode 14. Cathode 12 is the source of electrons and issupplied with heating current from a filament voltage supply, not shown.An accelerating voltage is supplied to cathode 12 from a source, notshown of adjustable high negative direct current voltage. The anode 14is connected to the casing of electron beam welder 10, which isgrounded. The difference in potential between cathode 12 and anode 14causes electrons emitted from the cathode to be accelerated throughanode 14 as shown by the dotted lines. Control electrode 13 is normallymaintained at a voltage, which is more negative than the voltage appliedto cathode 12. The magnitude of this bias, or voltage difference,controls the beam current in the same manner as the grid in an ordinaryvacuum tube controls triode plate current.

The electron optics of the embodiment shown herein consist of adjustmentcoils 17 and 18, tungsten diaphragms 19 and 21, the main electromagneticfocusing lens 22 and coil 23 for electron beam deflection.

Preferably, focusing of the electron beam by means of the electronoptics system enables concentration of the electron beam at its focalpoint in a very small spot having a diameter of approximately 0.010 inchat maximum power and less than 0.005 inch at lower powers. An opticalviewing system 24 is provided for convenience of the operator.

The focal point of the high energy density electron beam is produced inwork chamber 26 at some point at which the workpiece being cut islocated for the cutting action. For purposes of this invention theworkpiece is held in the vise 27 resting upon table 28. Table 28preferably is movable both in the longitudinal and transverse directionsand may also be provided with a tilting, rotary motion. The mechanismsrequired for moving table 28 from outside the work chamber 26 are notshown, because such means are conventional.

In accordance with this invention vise 27 is of special construction asshown in FIG. 2. To enable coaction with the electron beam 29 themicro-stream gas lance 30 is mounted within chamber 26 so that a veryfine gas stream 31 emitted from needle-like point 32 impinges exactlyupon the focal point 33 of electron beam 29.

The entire internal volume of electron beam welder is kept under vacuumby means of the vacuum pumping system 34, generally comprising amechanical pump (not shown) connected in series with a high-speed oildiffu sion pump (not shown). Preferably a vacuum shut-off valve 35 isprovided in a conduit interconnecting work chamber 26 and electron gun11 in addition to ball valve 35a in the column of welder 10 wherebyelectron gun 11 can be isolated while the work chamber is open to theatmosphere. The high voltage power supply, the auxiliary power supplyand the control apparatus for both the vacuum exhaust system and theelectrical system are conventional and are not shown in the interest ofsimplicity.

The gas to be impinged upon the impact area of the electron beam will beof particular value, if it actually chemically or catalytically promotesthe cutting action. In the case of the cutting of diamonds, oxygen ispreferred because it is effective at about 300 C., while carbon dioxideoxidizes diamond at about 1200 C. The gas under pressure is admitted tothe system from tank 36 with the admitting pressure being controlled bymetering valve 37. Although it is not shown in the drawing, work chamber26 will ordinarily have a viewing window to enable the operator toobserve the process being conducted within work chamber 26.

Steigerwald US. 2,793,281 (FIG. 9) discloses apparatus for the drillingof holes in diamond crystals by the use of a high energy density focusedbeam of electrons in an oxygen atmosphere with the oxygen being admittedto occupy the entire chamber wherein the electron stream impinges uponthe diamond crystal workpiece. Unfortunately, however, the apparatusdisclosed requires the use of a multi-chambered vacuum vessel with theentire vacuum vessel requiring a series of at least three exhaust(vacuum pumping) systems in order to differentially pump the severalchambers thereof. Such construction involves considerable initial costand its successful operation demands sufiicient of the operatorsattention to control the vacuum pumps that little time is available tothe operator for observing the cutting or drilling operation. As anillustration, without the benefit of the invention disclosed herein, thetechnician wishing to cut or drill diamonds with an apparatus such as isdisclosed in FIG. 1 would have to modify this apparatus by adding atleast two extra vacuum pumping systems including the requisite exhaustducts, seals, valves and vacuum instrumentation for these additionalvacuum systems in order to cut diamonds by known teachings. Further, theextreme criticality of the placement of the diamond crystal in the priorart apparatus relative to the opening through which the electron beamenters the working chamber is obviated by the practice of thisinvention.

Thus, by the use of the process and apparatus disclosed herein theinvestment in equipment and operating expense is considerably reducedand wide variations in oxygen concentration, beam current and potentialmay readily be employed in order to best accommodate the cutting ofvarious substances. As described herein above, a simple single chambervacuum system serviced by a single vacuum pumping system maysuccessfully be employed, because of the use therewith of multiplefunction vise 27 and the highly localized gas flow 31 provided by gaslance 32.

The vise 27 is particularly adapted to holding a nonconductin workpiece,such as an ordinary diamond crystal, in the position shown whereby theelectron beam 29 and the highly concentrated gas flow 31 may beaccurately superimposed. Massive copper jaws 41, 42 and 43, 44 are shownholding a diamond crystal 46 with these jaws serving simultaneously as aheat sink to quickly conduct away any heating effect contributed todiamond 46 by the electron beam and also as a Faraday cage around thediamond. Copper clamping plates 41 and 43 are adjustable relative to thecopper block base 47, which provides shoulders 42, 44 to coact withplates 41, 43. Preferably, the jaws have only a narrow gap between thembut extend up fom about inch to about /2 inch above diamond crystal 46.Cavity 48 extending through base 47 serves as an effectiveelectron-trapping cage.

During the cutting of nonconductive material, it is important that thematerial be firmly held by the coacting jaws of vise 28 to prevent anymovement of the crystal as the result of an electrical chargeaccumulated thereon during the bombardment. The Faraday cage effect, ofcourse, minimizes the charging up of crystal 46 thereby rendering moreeffective the cutting action of the electron beam. Single crystal,near-gem quality stones and industrial carbonados as well as sintereddiamond compacts have been successfully and quickly cut employing theprocess and apparatus of this invention.

In the cutting operation the nonconductive diamond crystal 46 is fixedin vise 27, which in turn is placed upon table 28 in the proper positionfor focusing the electron beam 29 between the jaws of vise 27. The workchamber pressure should be kept low enough to prevent arcing around theelectron gun structure caused by continued cutting. After the vacuum hasbeen drawn in the working chamber 26, electron beam 29 is initiated andfocused. If it is desired to drill a hole through crystal 46, table 28is not moved; if it be desired to make a cut through crystal 46, thecutting action is obtained simply by moving table 28 (and therebydiamond 46) relative to beam 29.

If the cutting of the diamond 46 is conducted in the absence of themicrojet 31 of oxygen, the cut face of the diamond, which resembles theappearance of flame-cut steel, indicates the formation of graphitethereon. However, graphite does not form at any other place on diamondcrystal 46.

When the stream 31 of oxygen is employed the debris generated duringelectron bombardment is quickly removed from the cut surface of thestone leaving a smoother surface than is the case with cuts produced inthe absence of oxygen. Also, the cutting rate is increased by a factorof about 5. As an example, a l-carat gem can be cut by the use of thisinvention in about 10 minutes. To compare this last mentioned cuttingaction with the conventional sawing of a diamond crystal, a gem of thissize may take as long as eight hours to saw. Further, when the gas lanceis employed, the beam current and potential may be reduced to somedegree thereby reducing the amount of crystal lost during the cuttingaction. As an example, in the cutting of diamonds with electron beamcutting at k.v. supplemented with the oxygen lance having a flow ratefor oxygen of as little as 0.03 cubic feet per hour, it was found thatthe beam current could be reduced from 10 milliamperes to less than 1milliampere. Also, in the cutting of diamonds, in the absence of flowfrom the gas lance the electron beam must be employed at a slow pulserate in order to minimize crystal breakage, while the addition of thegas output from the lance enables substantially continuous smoothcutting by pulsing the electron beam at a very rapid rate i.e. about 35c.p.s. This last factor, of course, is particularly important withrespect to increasing the rate of cutting.

The manner in which the impinging gas stream is supplied to focal point33 is important and it is preferable to use a cylindrical expansionnozzle (such as a hypodermic needle) having a large length/radius ratiogreater than about 10:1 and located at a distance from the point ofelectron beam impingement such that the radial spreading of the gasstream does not exceed about twice the nozzle outlet diameter.

The construction of the gas lance or gas jet device in the form of asimple, narrow expansion nozzle makes the operation of the apparatuseasy to achieve over a wide pressure range in the working chamber. Inparticular, it makes for flexibility in setting process conditions,especially in the rate of oxygen, or other gas delivery, withoutinterfering with the passage of electrons to the point of electron beamimpingement and without the necessity of adhering to very specific andrigid spacing requirements. All that is necessary in the practice ofthis invention is that the expansion nozzle be so dimensioned that thegas leaving the nozzle is able to make the transition from viscous tomolecular flow, thereby giving appreciable direction and form theretoand permit-ting predictability of the extent of spread of the flow to anaccuracy of at least about 50 percent. In the case of a cylindricalnozzle, as noted above, the length/radius should be about :1 or greater.Because of this design criterion the criticality of the placement of theend of the nozzle relative to the work point is considerably diminished.The data for the selection of particular length/radius ratios orequivalent parameters in the case of non-cylindrical nozzles may befound by referring to the textbook, Scientific Foundations of VacuumTechnique by S. Dushman (2nd edition, 1962, John Wiley and Sons Inc.) inchapter 2, Flow of Gases Through Tubes and Orifices.

The only restriction on the quantity of gas flow through the nozzle isthat it be proportioned to the overall capacity of the pump system. Thedevice disclosed herein has been successfully operated when the pressurein the manifold of the vacuum pumping system a short distance from theworking chamber is of the order of 10 microns of mercury. The capacityto operate at such low pressures (pressures even lower than theaforementioned may be used) is due to the particular mode of gasdelivery and is particularly advantageous in promoting longer filamentlife for the electron source.

This new and relatively inexpensive apparatus and technique, with itsfaster, smoother cutting action and lowering of thermal stresses willrender the shaping of diamonds already set in tool shanks economicallyattractive by enabling the ready readaption of such a diamond tool toany desired use. Further, using this invention, small slices may bequickly removed from natural diamonds to ascertain whether there may behigher quality diamond material within the stone than appears from aview of the outer surface.

Various modifications are contemplated and may obviously be resorted toby those skilled in the art without departing from the spirit and scopeof the invention, as hereinafter defined by the appended claims, as onlya preferred embodiment thereof has been disclosed.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. In an apparatus for electron beam cutting comprising an electronemitter, means for focusing at a location removed from said emitter abeam of electrons emitted from said electron emitter, said focusingmeans being constructed to recollect said focused electrons into acylindrical region of increased current density, a working chamberwithin which said cylindrical region is focused, means for evacuatingsaid working chamber and said electron emitter and means in said workingchamber for positioning a material to be cut at said cylindrical region,

9 the improvement in said positioning means comprising a vise having abase portion and adjustable clamping means supported thereon forcoaction therewith located in said working chamber for holding andsubstantially enclosing an electrically nonconducting material to be cutbetween said base portion and said clamping means, said base portion andclamping means being made of a met-a1 having a high rate of thermal andelectrical conductivity, and said base portion having formed therein anelectrontrapping cavity and a slot placing said electron-trapping cavityin communication with the region of coaction between said base portionand said clamping means.

2. The improvement substantially as recited in claim 1 wherein the viseis made of copper.

3. In an apparatus for electron beam cutting comprising an electronemitter, means for focusing at a location removed from said emitter abeam of electrons emitted from said emitter, said focusing means beingconstructed to recollect said focused electrons into a cylindricalregion of increased current density, a working chamber within which saidcylindrical region is focused, means for evacuating said working chamberand said emitter and means in said working chamber for positioning amaterial to be cut at said cylindrical region, the improvementcomprising in combination:

(a) a vise having a base portion and clamping means supported thereonfor coaction therewith located in said working chamber for holding andsubstantially enclosing an electrically non-conducting material to becut between said base portion and said clamping means, said base portionand clamping means being made of a metal having a high rate of thermaland electrical conductivity, and said base portion having formed thereinan electron-trapping cavity and a slot placing said electron-trappingcavity in communication with the region of coaction between said baseportion and clamping means, and

(b) a gas lance supported within said working cham bet and directedtoward the focal point of said cylindrical region for impinging aconcentrated stream of gas upon the cylindrical region of increasedcurrent density.

4. The improvement substantially as recited in claim 3 wherein the gaslance is a cylindrical expansion nozzle having a length/radius ratiogreater than about 10.

5. The improvement substantially as recited in claim 4 with the nozzleoutlet of the gas lance located at a distance from the focal point ofsaid cylindrical region such that the radial spread of a gas streamemitted therefrom does not exceed about two times the diameter of thenozzle at the outlet thereof.

References Cited UNITED STATES PATENTS 2,793,281 5/1957 Steigerwald.

3,009,050 11/1961 Steigerwald 2l9121 3,033,974 5/1962 Schleich et al.219121 3,113,201 12/1963 Stepath 219 3,187,216 6/1965 Sciaky 2191213,250,842 5/1966 Hikido 219121 3,324,277 6/1967 Herring 219-69 3,340,3779/1967 Okazaki et al. 2l9121 RICHARD M. WOOD, Primary Examiner.

W. D. BROOKS, Assistant Examiner.

US. Cl. X.R. 21969

